SiC (silicon carbide) is superior in heat resistance and mechanical strength than an existing semiconductor material such as Si (silicon) and GaAs (gallium arsenide), and also has good high-temperature properties, high-frequency properties, dielectric strength, and resistance to environments. In addition, it is easy to perform the valence control of electrons and holes by doping an impurity. Moreover, SiC has a wide band gap (for example, single crystal 6H-SiC has a band gap of about 3.0 eV, and single crystal 4H-SiC has a band gap of 3.26 eV). For these reasons, single crystal SiC receives attention and is expected as a semiconductor material for a next-generation semiconductor material for a power device.
As a method of producing (growing) single crystal SiC of this type, conventionally, known are the Achison method which is generally known as an industrial method of producing an SiC abrasive material, and the sublimation and recrystallization method in which powder SiC produced by the Achison method is used as a raw material and a crystal is grown on a single crystalline nucleus.
In the Achison method of the above-described conventional production methods, however, a single crystal is grown slowly over a long time period, so that the crystal growth rate is very low. In addition, a large number of crystalline nuclei are generated in an initial growth stage, and they propagate to an upper portion of the crystal as the crystal growth advances. Thus, it is difficult to singly obtain a large-size single crystal.
In the sublimation and recrystallization method, a high-speed growth of about 1 mm/hr. is adopted mainly for an economical reason (production cost), so that impurities and pin holes which have a diameter of several microns and which pass through the crystal in the growing direction are likely to remain in a growing crystal. Such pin holes are called micropipe defects and cause a leakage current when a semiconductor device is fabricated. Accordingly, there exists a problem in that single crystal SiC having a sufficiently good quality cannot be obtained. This blocks a practical use of SiC which has many superior characteristics as compared with other existing semiconductor materials such as Si and GaAs as described above.